1. Field of the Invention
The present invention relates to thin-film magnetic heads for writing used in floating magnetic heads. In particular, the present invention relates to a thin-film magnetic head which is suitable for narrower tracks and which can suppress write fringing. The present invention also relates to a method for making the thin-film magnetic head.
2. Description of the Related Art
FIG. 13 is a partial front view of a conventional thin-film magnetic head viewed from a face opposing a recording medium, the air bearing surface (ABS). This thin-film magnetic head is an inductive write head. A MR read head may be provided under this inductive head.
The inductive head has a lower core layer 1 and an insulating layer 9 formed of an insulating material such as SiO2 on the lower core layer 1. The insulating layer 9 has a groove 9a. A lower magnetic pole layer 3, a magnetic gap layer 4, an upper magnetic pole layer 5, and an upper core layer 6 are formed, in that order, in the groove 9a. The lower magnetic pole layer 3 is magnetically coupled with the lower core layer 1, whereas the upper magnetic pole layer 5 is magnetically coupled with the upper core layer 6.
The groove 9a has a base section having a track width Tw and an upper section having sloping faces 9b which gradually converge from a surface 9c of the insulating layer 9 in the track width direction. The upper core layer 6 is formed over the upper magnetic pole layer 5 and the sloping faces 9b. 
FIGS. 14 to 16 show steps for making the thin-film magnetic head shown in FIG. 13. With reference to FIG. 14, the insulating layer 9 is formed on the lower core layer 1 and then a resist layer 7 is formed thereon. The resist layer 7 is exposed and developed to form a predetermined gap 7a by patterning. The gap 7a is formed in the perpendicular direction (in the Z direction in the drawing) to the lower core layer 1 and has a constant width Tw. The exposed portion of the insulating layer 9 is etched by a reactive ion etching (RIE) process to form the groove 9a having the width Tw. Thus, the track width Tw is defined by the width of the gap 7a formed in the resist layer 7.
With reference to FIG. 15, the resist layer 7 is removed and then a resist layer 8 having a gap 8a which is larger than the groove 9a is formed on the groove 9a by a patterning process. The resist layer 8 has a thickness H1. Since the thickness H1 of the resist layer 8 is larger than the width Tw of the groove 9a in the insulating layer 9, the surfaces 9c of the insulating layer 9 are partially exposed in the gap 8a. 
With reference to FIG. 16, the surfaces 9c of the insulating layer 9 are obliquely etched by ion milling to form the sloping faces 9b. 
In the thin-film magnetic head which is formed by the steps shown in FIGS. 14 to 16 and which is shown in FIG. 13, the track width Tw can be formed to be 1.0 xcexcm or less. Moreover, the upper core layer 6 is formed on the sloping faces 9b in the groove 9a of the insulating layer 9. Thus, the upper core layer 6 is properly distant from the lower magnetic pole layer 3 which is magnetically coupled with the lower core layer 1 so that write fringing is effectively prevented.
This conventional thin-film magnetic head, however, is suitable for future narrower track widths. The width (resolution) of the gap 7a formed by the patterning step shown in FIG. 14 significantly depends on the wavelength used in the exposure and developing process. The shorter the wavelength, the higher the resolution. Since the resolution is limited, the gap 7a cannot have a width which is smaller than the resolution limit.
As described in the patterning step shown in FIG. 14, the width of the groove 9a defining the track width Tw is substantially the same as the width of the gap 7a formed in the resist layer 7 by patterning. In the method for defining the track width Tw, which transfers the gap 7a to the groove 9a using the RIE process, a track width Tw which is smaller than the width of the resist layer 7, which is limited by the resolution, cannot be formed.
In the ion milling step shown in FIG. 16, the incident angles xcex81 and xcex82 of ions entering from the right and left sides, respectively, in the drawing are different from each other due to an uneven ion distribution. As a result, the tilted angles of the sloping faces 9b are different between the left and the right, and these sloping faces 9b are not symmetrically arranged.
As the track width Tw is decreased, the imbalance between the tilted angles of the sloping faces 9b is significant when the resist layer 8 on the insulating layer 9 is unevenly distributed or when the resist layer 8 has a large thickness H1.
Referring to FIG. 13, when the tilted angles of the right and left sloping faces 9b are different from each other, a fringing magnetic field will be easily generated between the upper core layer 6 on the sloping faces 9b and, for example, the lower magnetic pole layer 3 magnetically coupled with the lower core layer 1. As a result, write fringing cannot be effectively prevented.
It is an object of the present invention to provide a thin-film magnetic head which has a track width Tw smaller than the resolution of a resist and which effectively prevents write fringing.
It is another object of the present invention to provide a method for making the thin-film magnetic head.
According to an aspect of the present invention, a thin-film magnetic head includes: a lower core layer, the lower core layer optionally having a lower magnetic pole layer thereon; an upper core layer, the upper core layer optionally having an upper magnetic pole layer thereunder; at least one insulating layer disposed between the lower core layer and the upper core layer, the insulating layer having a groove for defining a track width; at least one of the lower magnetic pole layer and the upper magnetic pole layer being provided in the groove; and a magnetic gap layer provided between the lower core layer and the upper core layer. The insulating layer includes at least one primary insulating layer lying at the lower core layer side and at least one auxiliary insulating layer formed on the primary insulating layer, the groove is formed at least in the primary insulating layer, the auxiliary insulating layer has sloping faces gradually diverging in the track width direction from both top edges of the groove to the surfaces of the auxiliary insulating layer, and the upper core layer is formed on the sloping faces.
In the present invention, the primary insulating layer is formed on the lower core layer and the auxiliary insulating layer is formed thereon. The auxiliary insulating layer has the groove for defining the track width Tw. The track width Tw is smaller than the resolution of a resist, and is preferably not more than 0.7 xcexcm, more preferably not more than 0.5 xcexcm, and most preferably not more than 0.3 xcexcm.
Moreover, the auxiliary insulating layer has sloping faces which gradually diverge in the track width direction from both top edges of the groove to the surfaces of the auxiliary insulating layer. The upper core layer, which may include the upper magnetic pole layer, is formed on the sloping faces. Since the sloping faces are symmetrically formed, write fringing is effectively prevented.
The sloping faces may be formed by etching the auxiliary insulating layer or by forming the auxiliary insulating layer by a sputtering process.
Preferably, the etching rate of the primary insulating layer in reactive ion etching is higher than the etching rate of the auxiliary insulating layer.
Preferably, the primary insulating layer comprises at least one insulating material selected from the group consisting of Al2O3, SiO2, Ta2O5. Preferably TiO, AlN, AlSiN, TiN, SiN, NiO, WO, WO3, BN, CrN, and SiON, and the auxiliary insulating layer comprises at least one insulating material selected from the group consisting of Al2O3, Si3N4, AlN, and SiON.
In this combination of the insulating materials, the etching rate of the primary insulating layer becomes higher than the etching rate of the auxiliary insulating layer.
More preferably, the etching rate of the primary insulating layer is at least ten times higher than the etching rate of the auxiliary insulating layer. In order to satisfy this condition, it is preferable that the primary insulating layer comprise at least one of SiO2 and SiON and the auxiliary insulating layer comprise at least one of Al2O3 and Si3N4.
According to another aspect of the present invention, a method for making a thin-film magnetic head includes the steps of:
(a) forming at least one primary insulating layer on a lower core layer,
(b) forming at least one auxiliary insulating layer using an insulating material having an etching rate which is lower than the etching rate of a material for the primary insulating layer in reactive ion etching,
(c) forming a resist layer having a predetermined gap on the auxiliary insulating layer,
(d) etching the auxiliary insulating layer exposed by the gap by an ion milling process to form sloping faces which converge toward the lower core layer in the track width direction,
(e) removing the resist layer,
(f) etching the primary insulating layer exposed between the sloping faces by a reactive ion etching process to form a groove defining a track width in the primary insulating layer,
(g) forming a magnetic gap layer on one of the lower core layer and a lower magnetic pole layer which is optionally formed on the lower core layer in the groove, and
(h) forming an optional upper magnetic pole layer on the magnetic gap layer within the groove and then forming an upper core layer on one the upper magnetic pole layer and the magnetic gap layer.
As described above, the primary insulating layer and the auxiliary insulating layer are formed on the lower core layer. The resist layer having the gap is formed on the auxiliary insulating layer by patterning. The width of the gap in the resist layer significantly depends on the wavelength of light used in an exposure and developing process. For example, when i-line light (wavelength is 365 nm) is used, the gap can be reduced to approximately 0.4 xcexcm.
However, a gap having a width of less than 0.4 xcexcm cannot be formed using the i-line light. In a conventional method shown in FIG. 14 for defining the track width Tw by ion milling transfer of the gap formed in the resist layer to the groove formed in the insulating layer, a track width Tw which is smaller than 0.4 xcexcm is not formed using the i-line light.
In the present invention, a resist layer having a gap with a predetermined width is formed on the auxiliary insulating layer. The auxiliary insulating layer exposed in the gap is etched by an ion milling process in the step (d). The etching forms sloping faces which converge in the track width direction toward the lower core layer, at both sides of the groove formed by the etching.
Thus, the bottom width of the groove in the auxiliary insulating layer is smaller than the gap width of the resist layer. When the gap width of the resist layer is, for example, 0.4 xcexcm which corresponds to the resolution of the i-line light, the bottom width of the groove in the auxiliary insulating layer is smaller than 0.4 xcexcm.
According to the method of the present invention, the groove formed in the auxiliary insulating layer can have a bottom width which is smaller than the resolution of the i-line light.
In the step (f) of the method according to the present invention, the primary insulating layer is etched substantially in the vertical direction by the reactive ion etching process so as to form a groove having a width which is the same as the bottom width of the groove in the auxiliary insulating layer. The width of the groove formed in the primary insulating layer is defined as the track width Tw. The etching rate of the insulating material used for the primary insulating layer is larger than the etching rate of the insulating material for the auxiliary insulating layer. The bottom width of the groove in the auxiliary insulating layer is smaller than the resolution of the light used in the exposure and developing process for the resist. Consequently, the width for defining the track width Tw of the groove in the primary insulating layer is smaller than the resolution. Thus, the track width Tw in the present invention is smaller than the resolution. Accordingly the thin-film magnetic head is suitable for future narrower tracks required for higher recording densities.
In the step (c), the resist layer is preferably formed on the auxiliary insulating layer so that the thickness of the resist layer is in a range of one to three times the width of the groove. The sloping faces of the auxiliary insulating layer thereby have a desired shape which can effectively prevent write fringing.
Preferably, in the step (c), the resist layer is exposed and developed to form the gap, and is then heated to form the sloping faces converging toward the lower core layer in the track width direction at both sides of the gap.
Alternatively, the above method for making a thin-film magnetic head further includes the steps of, instead of the steps (b) to (e):
(i) forming a lift-off resist layer having indented sections at the bottom thereof on the primary insulating layer,
(j) depositing an auxiliary insulating layer in the indented sections of the resist layer and on the primary insulating layer by a sputtering process using an insulating material having an etching rate which is lower than the etching rate of an insulating material for the primary insulating layer in reactive ion etching, and simultaneously forming sloping faces to form sloping faces converging toward the lower core layer in the track width direction, and
(k) removing the resist layer.
As described above, the resolution of the i-line light in the exposure and developing process for the lift-off resist layer is 0.4 xcexcm. Thus, the width of the top face of the lift-off resist layer on the primary insulating layer is at least 0.4 xcexcm.
However, the lower portions of the lift-off resist layer are eroded during the exposure and developing process and indented sections are formed at the lower portions. Thus, the bottom width of the lift-off resist layer is smaller than the resolution.
The auxiliary insulating layer is formed by a sputtering or ion beam sputtering process in oblique directions so that the auxiliary insulating layer extends to the interior of the indented sections. As a result, the auxiliary insulating layer has a gap width which is smaller than the resolution.
In the subsequent step (f), the groove for defining the track width Tw which is smaller than the resolution can be formed in the primary insulating layer. Preferably, the primary insulating layer is formed of at least one insulating material selected from the group consisting of Al2O3, SiO2, Ta2O5, TiO, AlN, AlSiN, TiN, SiN, NiO, WO, WO3, BN, CrN, and SiON. Preferably the auxiliary insulating layer is formed of at least one insulating material selected from the group consisting of Al2O3, Si3N4, AlN, and SiON. In this combination, the etching rate of the primary insulating layer is larger than the etching rate of the auxiliary insulating layer.
Preferably, the etching rate of the insulating material for the primary insulating layer is at least ten times higher than the etching rate of the insulating material for the auxiliary insulating layer. In order to satisfy this condition, it is preferable that the primary insulating layer be formed of at least one of SiO2 and SiON and the auxiliary insulating layer be formed of at least one of Al2O3 and Si3N4.
In this case, the primary insulating layer is selectively etched in the reactive ion etching process for forming the groove for defining the track width in the primary insulating layer, while the auxiliary insulating layer is not substantially etched. As a result, the groove for defining the track width can be formed in the primary insulating layer so that the width of the groove is substantially the same as the bottom width of the groove in the auxiliary insulating layer. This small track width Tw is suitable for narrower tracks.